1. Field of the Invention
The present invention relates to a process for the preparation of high molecular weight organopolysiloxanes by the polymerization and rearrangement of low molecular weight organopolysiloxanes in the presence of a catalyst comprising sulfonic or phosphonic acid functions.
2. Description of the Prior Art
A wide variety of processes are known to this art to polymerize and rearrange low molecular weight organopolysiloxanes by acid catalysis, the polysiloxanes being linear and/or cyclic.
These catalysts containing sulfonic acid groups which to date have been used generally consist of cation exchange resins. Thus, U.S. Pat. No. 3,322,722 (Dow Corning) features a batch process for the rearrangement of mixtures of organosilocon compounds containing siloxane, alkoxysilyl and acyloxysilyl linkages, the process being carried out in the presence of a strong acid catalyst, such as the commercial sulfonated resins (Amberlyst 15 and the like.) On catalysts of this type, the siloxane, alkoxysilyl and acyloxysilyl linkages are simultaneously rearranged.
French Patent No. 2,111,629 (Union Carbide) describes a process for the preparation of high molecular weight polysiloxanes by the continuous polymerization and rearrangement of relatively low molecular weight polysiloxane charges, the siloxane charges being passed over a bed of cation exchange resin of the macro-crosslinked sulfonic acid type, having an average pore volume of at least 0.01 cm.sup.3 /g and preferably of more than 0.03 cm.sup.3 /g. Macro-crosslinked sulfonic acid resins are described in U.S. Pat. No. 3,037,052. The best results are obtained with Amberlyst 15.
Nonetheless, need exists in this art for improved sulfonic acid catalysts permitting a further increase in productivity, and principally for processes to be carried out continuously (such productivity being expressed, for example, as kg of siloxane charge polymerized and rearranged per hour and per liter of catalyst).